Habitat-driven convergence in a Southern African freshwater crab clade (Decapoda: Potamonautidae: <i>Potamonautes</i> ) as evident from phylogenetic and morphometric data

Abstract During the present study, possible convergent evolution among 18 species of the southern African freshwater crab genus Potamonautes (MacLeay, 1838) in three distinct ecotypes was explored. DNA sequence data derived from three mitochondrial loci and one nuclear locus were used to construct a phylogeny generated with maximum likelihood and Bayesian inference approaches. The resultant phylogeny was subsequently compared to morphometric data derived from carapace and pereiopod variables. The three ecotypes, large-bodied riverine/lowland, small-bodied mountain stream, and burrowing species, were present throughout the phylogeny. When data for species belonging to the three aforementioned ecotypes are grouped, mountain stream living and burrowing species overlapped, while riverine/lowland species are morphometrically distinct. Convergence in morphological traits was assessed using ancestral state reconstruction, principal component analysis, phylogenetic generalized least squares (PGLS), and convergence similarity (C1, C2, and w) analyses. Convergent similarity analysis elucidated convergent morphological adaptations within each ecological grouping, with each ecotype demonstrating a significant degree of convergence. Interestingly, the PGLS analysis corroborated ecotype classification as important for species’ differences, irrespective of phylogeny. These findings highlight convergent evolution in response to habitat pressures. The present study, the first of its kind on freshwater crabs, suggests that taxonomic features, such as carapace and pereiopod characters, may have obscured evolutionary relationships.